FROM THIS EPISODE

The warning may or may not be real, but Russian state media say Ukraine must surrender Crimea tomorrow or face a "military storm." Russian troops have crossed the border, and it's not clear how far President Putin wants to go. Meantime, Ukraine's new government is asking support from the West. As President Obama considers his options in the middle of Europe, the issue's a game-changer for the humanitarian disaster in Syria, which is getting worse by the day We look at two international crisis points, where the US and Russia have critical roles to play.

Banner image: Military personnel, believed to be Russian servicemen, walk outside the territory of a Ukrainian military unit in the village of Perevalnoye outside Simferopol March 3, 2014. Photo: Baz Ratner/Reuters

Russian state media have issued threatening warnings today, which have subsequently been contested by the country's diplomatic officials. But Vladimir Putin has had nothing public to say, and officials of the new government in Ukraine are warning about the prospect of an invasion. If Russia does intend to forcefully take control of Crimea, it would violate international laws on territorial integrity. Already, the western powers have threatened various ways to isolate Russia diplomatically and economically. Does Vladimir Putin care?

UN Secretary General Ban Ki-Moon said today there must be a third round of peace talks between Syria and its divided opponents. The second round collapsed over disputes about the agenda, and some diplomats have declared the effort a failure. It was an agreement between the US and Russia that got the talks started, with each backing a different side. What's the impact of the Ukrainian crisis?